Through the nearly 800 years which Portugal was a monarchy, the kings held various other titles and pretensions. Two Kings of Portugal, Ferdinand I and Afonso V, also claimed the crown of Castile. When the House of Habsburg came into power, the Kings of Spain, and Naples, also became Kings of Portugal. The House of Braganza brought numerous titles to the Portuguese Crown, including King of Brazil and then Emperor of Brazil.

After the demise of the Portuguese monarchy, in 1910, Portugal almost restored its monarchy in a revolution known as the Monarchy of the North, though the attempted restoration only lasted a month before destruction. With Manuel II's death, the Miguelist branch of the House of Braganza became the pretenders to the throne of Portugal. They have all been acclaimed King of Portugal by their monarchist groups. This is purely symbolic and no one can have a place among the Kings of Portugal unless they were acclaimed by the Portuguese state and parliament. The Portuguese government states that the current representative of the House of Braganza, Duarte Pio, Duke of Braganza, is the legitimate successor to the Kings of Portugal, but only recognizes him as Duke of Braganza and not as King of Portugal.

The monarchs of Portugal all came from a single ancestor, Afonso I of Portugal, but direct lines have sometimes ended. This has led to a variety of royal houses coming to rule Portugal, though all having Portuguese royal lineage. These houses are:

The House of Habsburg, known as the Philippine Dynasty, is the house that ruled Portugal from 1581 to 1640. The dynasty began with the acclamation of Philip II of Spain as Philip I of Portugal in 1580, officially recognized in 1581 by the Portuguese Cortes of Tomar. Philip I swore to rule Portugal as a kingdom separate from his Spanish domains, under the personal union known as the Iberian Union.